This study investigated the role of carotid artery intima-media thickness (IMT) as a morphological marker of the response of vasculogenic erectile dysfunction (ED) patients to tadalafil, one of the phosphodiesterase 5 inhibitor (PDE5-I). Through March–December 2016, 51 men with vasculogenic ED aged over 30 years were enrolled in this prospective study. Vasculogenic ED was accepted as a normal testosterone level, with penile colour Doppler ultrasonography showing arteriogenic ED, venogenic ED or mixed arteriogenic and venogenic ED. All patients underwent biochemical and hormonal blood tests, ultrasonographic evaluation of the common carotid artery (CCA) IMT and penile colour Doppler ultrasonography. On-demand tadalafil (10 mg or 20 mg in cases of a non-response to 10 mg) was administered to each patient for 2 months. ED was assessed using the short form of International Index of Erectile Function (IIEF-5) before and after the drug therapy. According to the patients’ responses to the medication, they were grouped as non-responders or responders. Thirty-one of the 51 patients responded to tadalafil. The mean CCA IMT of the non-responders and responders was 0.9 ± 0.2 mm and 0.6 ± 0.2 mm, respectively (P = 0.000). The IMT of 90% of the non-responders was >0.67 mm, whereas it was >0.67 mm in 40% of the responders. The data were analysed using the Kolmogorov–Smirnov test, Chi-square test, t-test, Mann–Whitney U test and receiver operator characteristic (ROC) curves. Measurement of CCA IMT may offer an alternative and simple method to predict the response of vasculogenic ED patients to PDE5-Is.